The 13C south portal is decorated in the Gothic style. Inside, note the fine 16C gates by Juan Francés, the retable on the main altar devoted to the life of the Virgin, the Trascoro retable (16C) and the tomb of St Peter of Osma in multicoloured limestone (13C). In the museum, among the collection of old archives and illuminated manuscripts, there is a Beatus created in 1086 with many illustrations.